U.S. patent application number 10/212629 was filed with the patent office on 2004-02-05 for method and mold for molding plastic lenses.
This patent application is currently assigned to Essilor International Compagnie Generale d'Optique. Invention is credited to Boryslawski, Joseph, Reed, James A..
Application Number | 20040021238 10/212629 |
Document ID | / |
Family ID | 31187812 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040021238 |
Kind Code |
A1 |
Reed, James A. ; et
al. |
February 5, 2004 |
Method and mold for molding plastic lenses
Abstract
A method for making an organic glass lens or lens blank which
comprises providing a two-piece mold defining a molding cavity
having a vertical axis which is part of a fixed reference system
comprising said vertical axis and a horizontal axis which
intersects at the center of the mold, a liquid tight annular
closure member disposed at the periphery of the mold pieces for
maintaining the two mold pieces and closing the molding cavity,
wherein the annular closure member comprises at least a portion
thereof made of a material that is initially gas permeable but
becomes gas impermeable when in contact with a liquid polymerizable
composition.
Inventors: |
Reed, James A.; (Clearwater,
FL) ; Boryslawski, Joseph; (St. Petersburg,
FL) |
Correspondence
Address: |
Mark B. Wilson
Fulbright & Jaworski L.L.P.
Suite 2400
600 Congress Avenue
Austin
TX
78701
US
|
Assignee: |
Essilor International Compagnie
Generale d'Optique
147 rue de Paris
Charenton cedex
FR
94227
|
Family ID: |
31187812 |
Appl. No.: |
10/212629 |
Filed: |
August 5, 2002 |
Current U.S.
Class: |
264/2.2 |
Current CPC
Class: |
Y10S 425/812 20130101;
B29C 33/10 20130101; B29D 11/00413 20130101; B29D 11/00528
20130101; B29D 11/00538 20130101; B29C 33/0038 20130101; Y10S
425/808 20130101; B29C 39/26 20130101 |
Class at
Publication: |
264/2.2 |
International
Class: |
B29D 011/00 |
Claims
1. A method for making an organic glass lens or lens blank
comprising: providing a two-piece mold defining a molding cavity
having a vertical axis which is part of a fixed reference system
comprising said vertical axis and a horizontal axis which
intersects at the center of the mold, a liquid tight annular
closure member disposed at the periphery of the mold pieces for
maintaining the two mold pieces and closing the molding cavity;
filling the molding cavity from the bottom thereof with a liquid
polymerizable composition; evacuating outwardly the gas initially
contained in the molding cavity; polymerizing the liquid
polymerizing composition; and disassembling the mold and recovering
the molded lens or lens blank; wherein the annular closure member
comprises at the top of the molding cavity at least a portion made
of a material that is initially gas permeable but becomes gas
impermeable when contacted by the liquid polymerizable
composition.
2. The method of claim 1, comprising: almost totally filling the
molding cavity with the composition but leaving a gas bubble at the
top of the molding cavity between the liquid polymerizable
composition and the annular closure member; and applying a force
either on the mold or the annular closure member to increase
pressure inside the molding cavity and evacuate the gas bubble from
the molding cavity through the initially gas permeable portion of
the annular closure member until said portion contacts the liquid
polymerizable composition and becomes gas impermeable.
3. The method of claim 2, wherein the force is locally applied on
the annular closure member around the initially gas permeable
portion.
4. The method of claim 3, wherein the force is applied by a plunger
shaped to provide a contact between the plunger and the annular
closure member at the periphery of the initially gas permeable
portion.
5. The method of claim 1, wherein the closure member comprises a
liquid impermeable, gas impermeable portion, leaving an opening at
the top of the mold cavity and a portion, initially gas permeable,
but becoming gas impermeable when in contact with the liquid
polymerizable composition, covering the opening.
6. The method of claim 5, wherein both portions of the closure
member are adhesive tapes.
7. The method of claim 1, wherein the liquid polymerizable
composition is introduced in the mold cavity through a check valve
disposed at the bottom of the mold.
8. The method of claim 1, wherein the liquid polymerizable
composition is a room-temperature polymerizable composition.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns molding optical lenses, in
particular ophthalmic lenses, from a polymerizable synthetic
composition.
[0003] 2. Description of the Prior art
[0004] The traditional mold comprises two pieces, typically made of
mineral glasses, at the periphery of which is disposed an annular
closure member, such as a gasket or an adhesive tape, defining with
them the required molding cavity.
[0005] The conventional way to fill a two-piece mold as above is by
causing the molding material to flow into the molding cavity
through a casting opening provided for this purpose in the closure
member.
[0006] In at least partly automated process, the mold to be filled
is vertically aligned with a filling device adapted to deliver a
particular quantity of molding material through a nozzle.
[0007] One possibility with such a vertically oriented mold is to
fill the molding cavity by gravity only through a nozzle disposed
on the top of the mold periphery. See for example U.S. Pat. No.
5,110,514.
[0008] Experience has shown that unless special measures are
implemented, for example a relatively long waiting time (in the
order of two hours, for example) between filling the mold and
starting polymerization, the optical lenses obtained frequently
have localized optical defects of greater or lesser severity,
leading to relatively high reject rates.
[0009] To overcome the above problems, U.S. Pat. Nos. 5,547,618 and
5,662,839 propose filling the molding cavity of a two-piece mold
vertically oriented through a casting opening formed in a lower
part of the closure member and using pumping means adapted to cause
the molding material to flow without significantly pressurizing
it.
[0010] Typically, filling of the molding cavity is effected using a
pipe connected to a pressurized molding material reservoir and
applied, like a filling nozzle, to the casting opening.
[0011] The annular closure member, for example an adhesive tape,
must not only fixedly maintain the two pieces of the mold in the
required relative positions but also provide a leak-proof seal with
regard to the liquid polymerizable material for avoiding leakage of
the material of the periphery of the mold.
[0012] Conventional adhesive tapes used to form the annular closure
members are generally impervious both to the liquid polymerizable
material and gases.
[0013] During the filling of the molding cavity with the liquid
polymerizable material, over filling of the molding cavity shall be
avoided in order not to deteriorate adhesion of the peripheral
adhesive tape while gases shall be evacuated from the mold cavity
and entrapping of gas bubbles within the liquid polymerizable
material shall be avoided as much as possible.
[0014] Thus, when using a conventional peripheral adhesive tape as
the annular closure, an opening must be provided in an upper
position of the tape to allow venting of the gases. This venting
opening is typically formed by punching the adhesive tape with a
needle.
[0015] One of the main problems is to evacuate the remaining gas
from the mold without leakages of excess monomer by the venting
opening. In particular, when using a bottom filled mold, it is
difficult to vent out the last air bubble which is usually
entrapped at the top of the molding cavity, just beneath the
punctured portion of the adhesive tape. This is particularly the
case when molding negative power glasses.
SUMMARY OF THE INVENTION
[0016] Therefore, the aim of the invention is to provide a method
for molding an organic lens or lens blank, in particular an organic
ophthalmic lens or lens blank which overcomes the prior art
problems and specifically allows venting out of gases and in
particular of the last air bubbles at the top of the molding cavity
without risks of leakage of the liquid polymerizable
composition.
[0017] A further object of the invention is to provide a two-piece
mold for implementing the method according to the invention.
[0018] According to the invention, there is provided a method for
making an organic glass lens or lens blank which comprises:
[0019] providing a two-piece mold defining a molding cavity having
a vertical axis which is part of a fixed reference system
comprising said vertical axis and a horizontal axis which
intersects at the center of the mold, a liquid tight annular
closure member disposed at the periphery of the mold pieces for
maintaining the two mold pieces and closing the molding cavity;
[0020] filling the molding cavity from the bottom thereof with a
liquid polymerizable composition;
[0021] evacuating outwardly the gas initially contained in the
molding cavity;
[0022] polymerizing the liquid polymerizable composition; and
[0023] disassembling the mold and recovering the molded lens or
lens blank;
[0024] wherein the annular closure member comprises at the top of
the molding cavity (with regard to the fixed reference system) at
least a portion made of a material that is normally gas permeable,
typically air permeable but becomes gas impermeable when contacted
by the liquid polymerizable composition.
[0025] In a preferred embodiment, the molding cavity is almost
totally filled with the composition but leaving a gas bubble at the
top of the molding cavity between the annular closure member and
the liquid polymerizable composition. Then, one applies a force
either on the mold or the annular closure member to increase
pressure inside the molding cavity and evacuate the gas bubble from
the molding cavity through the initially gas permeable portion of
the annular closure member, until said portion contacts the liquid
polymerizable composition and becomes gas impermeable.
[0026] More preferably, the force is locally applied on the annular
closure member around the initially gas permeable portion.
[0027] Even better, the force is applied by a plunger shaped to
provide a contact between the plunger and the annular closure
member at the periphery of the initially gas permeable portion.
[0028] Preferably, the plunger has a head which is U-shaped.
[0029] Preferably, the air permeable portion has a porosity such
that it can sustain an air flow ranging from 0.5 to 400 cm.sup.3.
cm.sup.-2. s.sup.-1, preferably 5 to 40 cm3. cm.sup.-2.s.sup.-1
(volume of air passing through 1 cm.sup.2 of air permeable portion
during one second).
[0030] In a most preferred embodiment, the annular closure means
comprises a classical liquid and air impermeable adhesive tape
covering the periphery of the mold except a short top section
thereof which is covered by an adhesive tape portion which is
normally gas permeable, typically air permeable but becomes gas
impermeable when contacted by a liquid such as the liquid
polymerizable composition used for making optical lenses or lens
blanks and in particular ophthalmic lenses or lens blanks.
[0031] As indicated above, the gas permeable means is preferably an
adhesive tape. Such adhesive tapes are known by themselves and are
coated porous materials exhibiting gas, typically air, permeability
and are disclosed in U.S. Pat. No. 5,989,698 and U.S. Pat. No.
6,183,853.
[0032] A suitable adhesive tape exhibiting air permeability and
repellency to liquids is also commercialized by 3M Company under
the denomination "VENT TAPE.RTM.".
[0033] When using an annular closure means comprising a classical
liquid and gas impermeable adhesive tape having a top opening, the
opening is typically a slot having a length ranging from 2 to 15 mm
(depending on the thickness of the lens) and a width ranging from
0.1 to 5 mm.
[0034] Of course, then the gas permeable, adhesive tape portion is
sized to entirely tightly cover the opening and allow its adhesion
to the mold parts. The liquid and gas tight adhesive tape can be
any classical adhesive tape commonly used in the technical
field.
[0035] The liquid polymerizable composition may be any classical
composition used for making optical and ophthalmic lenses or lens
blanks, but is preferably a room temperature polymerizable or
curable composition.
[0036] Preferred liquid polymerizable compositions are disclosed in
U.S. Pat. No. 5,973,098 which is incorporated by reference.
Briefly, these compositions comprise (a) at least one
polyiso(thio)cyanate monomer, and at least one polythiol monomer;
or at least one episulfide and optionally one or more compounds
having two or more functional groups capable of reacting with
episulfide groups; and (b) a polymerization catalyst, wherein the
polymerization catalyst comprises an effective amount of a least
one salt of formula: 1 M m p + Y n -
[0037] wherein
[0038] M.sup.P+ is a cation selected from the group consisting of
alkaline metals, alkaline earth metals, transitions metals and
ammonium groups of formula NR.sup.+.sub.4 in which R is an alkyl
radical,
[0039] Y.sup.- is an anion such as the corresponding acid YH has a
pKa fulfilling the condition 0.5.ltoreq.pKa.ltoreq.14 with the
proviso that when the polymerizable compositions comprise an
episulfide compound and M.sup.P+ is an ammonium group, the
polymerizable composition also comprises an electro-donor
compound,
[0040] p is the valency of the cation, and
[0041] n=mxp.
[0042] As previously indicated, the molding cavity which is
vertically oriented is filled from the bottom with the liquid
polymerizable composition.
[0043] Bottom filling of the molding cavity can be effected using
any classical filling means. For example, filling is effected
through the use of a check valve and in particular a duck bill
valve. An embodiment of a duck bill valve is disclosed in EP
0.998.951. Other duck bill valves are commercialized by Vemay
Laboratories.
[0044] After curing and demolding, the check valve remains
imprisoned with the polymerized material. The recovered lens blank
is then trimmed to eliminate the valve in order to obtain a
finished lens.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The foregoing and other objects, features and advantages of
the present invention will become readily apparent to those skilled
in the art from reading of the detailed description hereafter when
considered in conjunction with the accompanying drawings
wherein:
[0046] FIG. 1 is a cross-sectional schematic view of a two-piece
mold for implementation of the method according to the invention;
and
[0047] FIGS. 2A to 2C are schematic views of the main steps of the
method according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0048] As shown in FIG. 1, there is represented in cross-section a
view of a two-piece mold 10 according to the invention.
[0049] The two-piece mold 10 comprises a front piece 11 and a back
piece 12, preferably made of mineral glass, and an annular closure
member 13, such as a classical adhesive tape, disposed at the
periphery of the two-piece 11, 12.
[0050] The two pieces 11, 12 and the annular closure member 13
define together a molding cavity 14 which, as represented in FIG.
1, is intended for molding an ophthalmic lens.
[0051] Classical adhesive tape 13a which is gas, typically air, and
liquid impermeable is adhered to the periphery of mold parts 11, 12
and covers the periphery of the molding cavity 14 except a small
portion at the top of the molding cavity 14. Closure member 13
further comprises a portion 13b covering the small portion at the
top of the molding cavity 14.
[0052] Portion 13b is made of a material that is normally gas,
typically air, permeable but becomes gas impermeable when contacted
with the liquid polymerizable composition used for making the lens
or lens blank. Preferably, portion 13a (see FIG. 2A) is made of an
adhesive tape such as a vent tape covering the opening and adhering
to the periphery of the mold parts 11, 12 and/or adhesive tape
13a.
[0053] The molding cavity 14 comprises an upper half and a lower
half symetrically arranged with regard to a central horizontal axis
HH of the mold 10, the mold being held vertically or on the edge,
i.e. with the molding cavity extending in the direction of a
vertical axis perpendicular to the central horizontal axis HH.
[0054] A check valve 15, in the embodiment of FIG. 1 a duck bill
valve, is arranged in an opening managed in the lower or bottom
part of closure member 13 in order to establish flow communication
from the outside of the mold 10 into the molding cavity 14.
[0055] As shown in FIG. 2A, liquid polymerizable composition 16 is
introduced into molding cavity through duck bill valve 15.
[0056] In use, duck bill valve 15 is connected through a pipe (not
shown) to a pressurized reservoir (not shown) containing the
polymerizable composition. A dosing valve (not shown) may be
connected between the pressurized reservoir and the pipe to control
the delivery of polymerizable composition to the duck bill valve
15.
[0057] As it is well known, the duck bill valve 15 is initially
closed and opens under the slight pressure exerted by the
composition 16 delivered from the reservoir, thus filling the
molding cavity 14.
[0058] As shown in FIG. 2B, molding cavity 14 is filled up with
composition 16 until only a small gas (typically air) bubble 17
remains at the top of the molding cavity 14, just beneath the gas
permeable portion 13b of closure member 13.
[0059] As shown in FIG. 2C, a U-shaped plunger 18 is then pushed
against closure member 13 and especially against adhesive tape 13a
and a pressure is applied around the air permeable portion 13b by
local deformation of the adhesive tape 13a, allowing gas to escape.
Gas permeable, portion 13b when contacting liquid polymerizable
composition 16 becomes gas tight. During deformation of adhesive
tape 13a, portion 13b, due to its gas permeability property, allows
gas bubble initially present at the top of the molding cavity to be
vented out.
[0060] Once the molding cavity is completely filled and no gas
remains, the mold can be handled carefully without leakages of
polymerizable composition.
[0061] Then the liquid composition 16 is thereafter polymerized, at
least partially, to obtain a handable lens blank.
[0062] Mold 10 can be disassembled as usual, generally leaving the
duck bill valve 15 imprisoned within the polymerized
composition.
[0063] The recovered lens blank can then be edge machined to
eliminate the duck bill valve 15 and to obtain a finished lens
having the required geometry.
* * * * *